The Mountain View, Calif., company is releasing a PC application for searching Microsoft Office documents, images, e-mail and Internet Explorer Web pages. The final version, in public beta for nearly five months, now includes search capabilities for video and music files, full PDFs and Web surfing history in three Web browsers, including the fast-growing Firefox.

It also includes a software developers kit, or SDK, so that outsiders can build new search plug-ins. Already, Google has built a plug-in to search conversations in chat software Trillian.

"Google desktop search stores a copy of everything you see," said Nikhil Bhatla, a Google product manager. "That can be extremely useful if, for example, an application crashes. With (the tool), you can get the text of that last document you were working on."

For that reason, security plays a bigger part in the full version. Because the tool had been able to index privacy-sensitive documents--against users' wishes--the final product avoids indexing those Word and Excel files that are password-protected, Bhatla said. It also allows people to block indexing of secure Web sites. Google previously had to update the software because of the potential for malicious hackers to capture some personal data.

Google has heavy competition in the consumer desktop arena. Not only have its top rivals, Yahoo and Microsoft's MSN, introduced similar tools recently, but a litany of upstarts have emerged to compete for Web surfers' attention. Some are even having success; Blinkx said Friday that its desktop-search tool is now fielding 100 million searches daily.

All the search companies are hoping to lock in new visitors with desktop applications because they believe it will help them drive more Web searches--and hence more advertising sales. Search-related advertising is expected to be worth between $4 billion and $5 billion this year.

For now, Google has no plans to display ads related to consumers' personal information, Bhatla said.

Still, the company is pressed to keep pace with rival innovations. Yahoo, for example, licenses technology from X1 Technologies for its desktop search tool that lets people narrow searches of e-mail text by typing only a single letter. Bhatla said Google is aware of improvements that can be made to Google Desktop.

Other additions to Google Desktop include support for searching e-mail in Netscape mail and Thunderbird. The tool is also available in Chinese and Korean.

Search experts applauded Google's SDK.

"It means that anybody who feels like it's not doing what they like can go out and build something extra for it," said Danny Sullivan, editor of industry newsletter SearchEngineWatch.com.